It is well known that the greatest cost of building a fiber-optic network is laying the fiber. Thus, when carriers lay fiber, they tend to lay fibers in which only some of the fibers carry data traffic, and the rest of the fibers carry no data (i.e., are dark). In addition to the dark fiber, many companies also lay dark conduit, i.e., empty pipes through which new fiber can be pulled based on future need. In principle, the current supply of bandwidth could outstrip demand by as much as 20 or 30 times. However, the laying of long distance fiber has caused carriers to neglect the metropolitan area networks. Accordingly, demand exists for bandwidth in the metropolitan areas. Out of 110 million homes in the United States, around 50 million have at least one computer. Of those homes, only 8.3 million had cable modems at the end of 2001, and only 3.4 million had DSL (digital subscriber line) service. That leaves a sizable market for high-speed Internet access (i.e., broadband, or connections greater than about 128 kilobits per second) untapped. Taking a page from the semiconductor industry, where Moore's law has the number of processors on a computer chip doubling approximately every 18 months, analysts speculate that optical networks will grow at a similar rate. Traffic should double every year for the rest of the decade (“Too Much Fiber?” Optics & Photonics News, March 2002, pp. 32–37).
One commonly cited reason for low customer broadband demand is that many people do not want to pay extra money to make their Internet go faster (“Broadband dream hits snag: Americans unwilling to pay premium for high-speed web access”, by Jon Van, Chicago Tribune, Nov. 12, 2001, Business Section pg. 6). Such cost-sensitive customers, as well as telephone and Internet users globally (particularly those in large metropolitan areas), would benefit from faster data connection rates at reduced costs. This means that the demand for bandwidth will continue to grow, and telecommunications companies will keep looking for ways to squeeze more data through the fiber optic pipelines and ultimately connect these pipelines to users in metropolitan areas.
One way to squeeze more data in a fiber optic pipeline and connect to metropolitan users is to implement an optical switching device that is fast, and costs little. Such a device, a multi-functional optical switch (e.g., optical wavelength division multiplexer, optical wavelength division demultiplexer, optical add-drop multiplexer and/or optical interconnect device) is described, for instance, in PCT International Application No. WO 01/06305.
Among other things, PCT International Application No. WO 01/06305 discusses gratings-based resonance coupling to transfer light between different waveguides, wherein the waveguides in which the gratings are present are comprised of second-order nonlinear optical (2°-NLO) polymers (see, e.g., in particular, Example 8). The '305 application describes that if a grating is designed for resonance coupling for the wavelength λ and angle θ, then a small bias across the grating (i.e., produced by applying voltage to the electrodes) will shift the resonance enough so that the coupling will not occur. If a grating is designed so that the coupling is slightly off resonance, a small bias across the grating will change the index of refraction of the 2°-NLO waveguide to “tune in” to the resonance condition for wavelength λ. This configuration, therefore, can act as a multiplexer (or, conversely, demultiplexer), as a modulator, a filter, and a reflector, among other things. The bandwidth of a given channel in the 1.5 μm optical communication band is typically a fraction of a nanometer. Therefore the active grating needs to tune over the range of a nanometer. PCT International Application No. WO 01/06305 describes and encompasses multi-grating devices. Many of the devices, depicted, however, employ a single grating to effect transfer between two waveguide layers. With use of a single grating for such transfer, switching of signal between layers may capture only a portion (e.g., either the front, middle, or tail end) of the signal, not its entirety.
U.S. Patent Application No. 2002/0009274 also describes tuning of the grating by means of a distributed Bragg reflector (DBR) tuning electrode (see, e.g., Example 7). This reference describes the use of this, and other, gratings in a waveguide amplifier and/or laser. By comparison, and apart from any considerations regarding tunability of devices, in optical communications systems, it frequently is necessary or desirable to adjust (with precision) optical signal levels entering various system components. Adjustment of optical signals (e.g., levels) can be achieved by incorporating optical attenuators or optical modulators into the optical circuits. Attenuators and/or modulators are known in the art (e.g., and are described, for instance, in U.S. Patent Application Nos, 2001/0046363, 2002/0018636, 2002/0048073, and 2002/0063942).
However, there exists a need in the art for polymer-based modulators and/or attenuators, e.g., particularly those that are adapted to interface with polymer-based optical devices, such as those described in PCT International Application WO 01/06305. Accordingly, the present invention provides an optical attenuator and/or modulator, especially a variable optical attenuator and/or modulator. These novel devices optionally can be employed to assist with and/or facilitate transfer of data, e.g., in a fiber optic pipeline. These and other objects and advantages of the present invention, as well as additional inventive features, will be apparent from the following description of the invention provided herein.